This invention relates to the field of shotguns and, more particularly, shotguns with interchangeable barrel tubes of varying gauge sizes.
Shotguns are designed to fire one or more relatively small pellets called shot through a barrel with a smooth bore. Shotguns can either have a single barrel, or can be double barreled with the two barrels placed either side-by-side or one over the other (over-and-under).
Shotgun bore sizes commonly range from 12 gauge, 16 gauge, 20 gauge, 28 gauge and 0.410 bore. Barrels can be formed with different choke patterns due to the size made in the outer or muzzle end of the barrel to control the pattern of shot as it leaves the shotgun barrel. Shotgun gauges and choke patterns are selected based on the type of shooting to be done.
Because many shooters like to compete in different competition classes, shotguns have been provided with interchangeable barrels of different gauges. Interchangeable choke tubes have also been developed to be placed in the outer end of the shotgun barrel so that the shot pattern can be changed depending on shooting conditions.
Because of the expense of additional barrels, attempts have been made to develop shotguns which have interchangeable barrel tubes that fit in a 12 gauge barrel. However, since such tubes add weight to a shotgun, which can either tire a shooter or throw off his or her aim, a carrier barrel has been developed to be used with a 12 gauge barrel so that interchangeable tubes can be used to change gauges instead of having a complete barrel for each gauge. One such attempt is shown and described in U.S. Pat. No. 4,989,359 where an over-and-under shotgun is provided with a 12 gauge barrel and a second carrier barrel which is capable of accommodating internal barrel tubes of various gauges that can be utilized with 16 gauge, 20 gauge, 28 gauge and 0.410 bore shells. In this way, only two barrels are necessary for a full range of shotgun gauges. A similar development is shown and described in U.S. Pat. No. 5,018,293.
These barrel tubes are formed in two separate sections, an enlarged diameter chamber section in which a shell is initially placed and an elongated barrel section through which shot travels after the shell is discharged. The chamber section is formed of a relatively high strength material such as stainless steel or a titanium alloy and the barrel portion, being subjected to lower forces than the chamber, is formed of a light weight metal such as an aluminum alloy.
The barrel tubes have inner bores which are compatible with the gauge to be shot and outer diameters with separate ferrels or support portions that engage the inner diameter of the carrier barrel.
Previously designed barrel tubes are relatively heavy, weighing from 14-19 ounces. Because of the number of targets shot during a competition, the weight of such tubes adds to shooter fatigue over a long period of time and makes use in a 12 gauge barrel undesirable, thus giving rise to the development of the relatively expensive carrier barrel described above.
Since these barrel tubes are relatively thin, it has been considered difficult to reduce their weight and still maintain the structural integrity of the tube when subjected to competition shooting. Therefore, it would be advantageous to provide lighter weight barrel tubes which are interchangeable within the barrel of a 12 gauge shotgun to eliminate the need for a carrier barrel and allow such tubes to be used with ease in a 12 gauge barrel.